Dwarven Berserker

The pitch sits in an inversion most aggressive creatures never attempt: a 1/1 that hits for one if it gets through, but swells to a 4/1 trampler the moment a defender steps in front of it. The buff fires on becoming blocked, which hands the timing to the defending player rather than the attacker. You never get to pick the moment; the trigger goes off whether the block was a chump, a gang, or a clean trade, and the trample makes even a lone small blocker bleed three damage anyway. That puts the defender in a genuine bind: leaving the 1/1 unblocked costs one, but blocking it costs more, and a player who lets it connect twice is letting a beater do beater work. The escape hatch belongs to anyone holding instant-speed removal, who can kill it in response to the trigger and eat nothing, since the block is already locked in by the time the +3/+0 reaches the stack. As red aggression goes, this charges a price for the act of blocking rather than the act of casting, a forerunner of the later "you don't want to block this" school that puts the combat decision back on the defender. The cost keeps it grounded: cheap enough to be a real threat, frail enough that any removal answers it whether or not the trigger has resolved.